View Full Version : TELEX 850 ANR, No batteries, 747 classic?

19th Oct 2004, 10:24
I am considering the Telex 850 ANR headset. It does not require batteries, but uses the power from the microphone jack: http://www.telex.com/aircraft/products.nsf/allpages/CB016057AE14089286256CEC005720B7

It requires a "hot mic" connector; to my knowledge where the microphone is constantly turned on but only connected to the aircraft box when you are keying. Apparently, it does not work on the MD80 series, but how about 747 classics?

Telex could not answer me about this, because they do not know about avionics in 747 classics.

To my knowledge they are more or less the same - can anyone here tell me if it is normal for the 747 classics to be "hot mike" as described above?

Thank you,

19th Oct 2004, 11:18
No, you have to select either int or RT, either on the column or at the ASP.

19th Oct 2004, 12:12
Spannersatcx, thank you for the quick reply.

What you say means it cannot be used for practal purposes? I gather if I am doing the radio, I have to switch on the box every time I want to talk to ATC then, and keep the yoke mike switch in the down position?

Tell me if you think it is possible, otherwise I will have to live with dragging batteries along ...

11th Nov 2004, 19:36
The classic 747 does not have a "hot" mic for the headphone jack. It is too bad that Telex has not made a constant power source for the 850 in that it is an extremely comfortable headset and the power requirements for the ANR circuitry is minimal.

11th Nov 2004, 20:17
Thank you for the reply.

What if the switch on the yoke is kept in the down position (when not transmitting), will that not keep the mike powered? Anyway, I bought the headseat, so I'll give it a try. If it doesn't work I'll make my own battery pack or think up something else.

12th Nov 2004, 14:59

I thought it was a mandatory requirement for Capt and F/O to have hot mic.

i.e there is always a mic input from these 2 positions for CVR.

This is the case for UK a/c above 11400kgs

That is my understanding of the term 'hot mic', I stand to be corrected however,

(puts on pith helmet and ducks to avoid incomming flack:} )

12th Nov 2004, 18:53
Mono, I hope you are correct, never thought of that. Thought that the CVR CAM's were seperate from the headsets (mounted in the dashboard somewhere).

12th Nov 2004, 19:19
The MIC and ANR are powered via the MIC bias. So you need a powered MIC socket for both the MIC and ANR to work.

If the audio system on your 747 classic is of the older type, and it probably is, then it is designed for dynamic MIC's and there will be no power in the MIC socket.

If it is designed for electrec MIC's then you should have no problem.

Pub User
12th Nov 2004, 23:00

The CVR records microphone conversations, so if you are speaking to your mate using the intercom it will record it. If you're not on intercom, but speaking loudly enough to be heard, then the area microphone will pick it up.

16th Nov 2004, 02:56
Sigh :hmm:

All modern large transport a/c are mandated to have a "hot mic" input to the CVR. The supply is from the Audio Selector Panel and is fed direct to the relevant channel of the CVR - EVEN IF THE MIC IS NOT KEYED - It's the law.

It was introduced because either during initial testing or as a result of various incidents (I'm not sure which) crew members conversations were found to be inaudible.

Just in case 20+ years of avionic experience was wrong I dashed out to one of oue 767's and, sure enough, mic inputs could be heard on the CVR even though no mic selection was made nor the mic keyed. A quick AMM check showed that this is one of the checks carried out when performing a full CVR system check.

This still does not answer LGB's original question. The answer depends on what mics the a/c was designed to be used with.

The term "hot mic" was coined in the days of the old carbon mics. Which, as they were supplied with a bias voltage all the time, actually became quite hot after a while. These mics were prone to becoming scratchy after a while as the carbon coagulated over time.
The other mic technology of the time was the dynamic mic. However output voltages of dynamic mics were very low and this made them suseptable to noise.
So in a true compromise along came the Amplified dynamic mic. These mics used a dynamic mic and amplified the output at source, so they still needed a power supply like carbon mics and they infact became a direct replacement.

Thread creep over :ok:

My personal opinion is that the ANR circuits should work, as most a/c (even the old 747classics) are configured for the amplified type microphone. So, as long as the CVR is fitted and complies with current requirements it should work.

I don't see why it doesn't work in MD80 series a/c, perhaps they use dynamic mic systems.

8th Mar 2005, 19:26
I have had a chance to test it briefly now, it works wonders (Telex Airman ANR 850)!

More extensive testing lies ahead, but it definately DOES work, and does so in a very convincing way. It is definately targeting cockpit noise from a jet, as testing on the ground takes less noise away - since the noise it has been set to cancel is not like normal indoor noises, but in the cockpit it was like the "hiss" noise wasn't there at all, until removing headset or turning the switch of course..

10th Mar 2005, 10:14
You are absolutely correct re the requirements for UK (and I think these days JAR) aircraft. However our American cousins are a bit behind in such things and rely on the area mic for non intercom/transmit voices. I think this is because a large proportion of US crews still use hand mics and speakers rather than headsets so there is no benefit.
You should hear the accident investigators complain:)

3rd Jun 2005, 17:20
The airline I fly for has aircraft with different background, one could easily say.

Therefore, the audio setup varies as well. Some even have the other jack type with power in, 5-pin I think. I do not have a converter for that jack.

Impedance varies apparently, and I have had luck in a -300 only. All the -200s I have tried have failed to work with headset, most of them doesn't even work with the ANR noise switch in OFF.

One of them even blocked the receive capability of the COM radio, only when it was connected. (I testet it on the ground).

I am amazed that there can be such a difference in headsets. Why could there not be some kind of standard for all headsets? How difficult is THAT really, there is one microphone and one or two speakers, but it seems there are many ideas of how to specify headsets and intercoms. This headset is TSO'd, for what it is worth.

Anyone wants to buy my TELEX ANR 850 then? It is hardly used, and it works perfectly - with the right aircraft that is. It works too well, so I am really sorry it didn't work on the aircraft that I fly.

Too bad, Telex, you couldn't inform me better as to what type of aircraft or com systems it works in when I contacted you, but you got yourself a sale anyway.

Ha, ha, grim hund dér ... på den anden side, altså ... fåggit!

steve zodiac
5th Jun 2005, 14:09

How much do you want for the headset? I fly B757/B767 so I take it that it should be OK in these aircraft? Does it have standard 2 jack connectors?

Please send me a private message.

6th Jun 2005, 11:12
Yes, it has the standard two-connector plugs.

I cannot guarantee it fits any particular aircraft.

I tried it in a 743 where it worked perfectly (but then I was deadheading, so I just tried it briefly from jump seat position). From certain 742s it did not work, as described above. I think it is something with the impedance, the specs can be found at http://www.telex.com/aircraft/products.nsf/pages/Airman_ANR_850.

I have found that many of our aricraft have installed ANR headsets anyway, but since I gather the intercom function is not widely used, one has an ear uncovered anyway. Too bad, many people do not realize how loud the noise is, and what the long term impact on your ears amounts to. Put on an ANR headset for 5 minutes or more, then take it off, and you will note how loud the noise is!

Other links:


At present, I will not sell at less than GBP 300, if I get no offer in that range, I'll keep it to test it on other aircraft.

7th Jun 2005, 12:18
Tjaa, nu kunne jeg jo sige Hvad sagde jeg . Men det vil jeg ikke. :p

7th Jun 2005, 19:50
Tjaa, nu kunne jeg jo sige Hvad sagde jeg . Men det vil jeg ikke.

Well, they worked in some of the aircraft, I guess it was the newer ones. I never got a final answer when I asked Telex.

It is not a matter of whether there is power for the ANR or not. It is rather a matter of impedance, and type of microphone. The Telex 850 can also work as a normal headset, that is if the ANR is turned off. But even with the ANR switch off, the result was the same in the aircraft where it didn't work.

All the 747 Classics have to my knowledge a dual switch for R/T (up) and internal, like ground, intercom etc. (down) The down position is usually not spring loaded, so when not talking to ground or PA, the entire crew could have headsets on both ears, using the intercom and with ANR headsets - leaving the R/T switch in the Intercom position (unless talking to ATC). This would for me be a higher comfort:

1) Less noise for both ears, hearing ability lasts longer (in life!), less tired
2) Better understanding of what the others are saying. The distance in the cockpit and the noise makes it necessary to talk quite loud, if one wants to be heard. With the intercom, it is much more quiet and you do not have to shout.

But then, the entire crew need to agree on that, as well as the headsets should work with ANR.

Anyway, I have made an agreement to sell my 850, but if I get to fly aircraft where the intercom is used and the 850 headset works, then I'll be buying one once again, because it is quite good, lightweight as well.